Getter devices are well known for their ability to absorb impurities. These devices are usually made with a porous sintered metallic alloy, typically consisting of barium, titanium, or zirconium. The porous structure of the getter allows gases to diffuse through pores within the material. Certain types of gas are absorbed to the inner parts of the getter body. Non-inert gases absorb to the inside of the getter, while inert gases do not. This quality makes the getter device ideal for ring laser gyroscope applications because a ring laser gyroscope usually employs inert gases for lasing. This holds true for other gas discharge applications, such as neon signs.
A ring laser gyroscope detects and measures angular rates by measuring the frequency difference between two counter-rotating laser beams according to the Sagnac effect. The two laser beams simultaneously circulate in the optical cavity of the gyroscope with the aid of mirrors to reflect each beam around the cavity. The laser beams will ideally have identical frequencies when the sensor is at rest. However, if the sensor is rotated, the beams will have different frequencies. This frequency difference is measured to provide the rate of rotation.
The optical cavity is filled with a gas that is excited by an electric current passing between the electrodes mounted on the block of the gyroscope. In a typical arrangement, a ring laser gyroscope has two anodes and one cathode mounted on the gyroscope block, but other applications employ different numbers of anodes and cathodes. When the electric potential becomes sufficiently large to create a population inversion within the lasing gas, a laser is generated. A typical lasing gas is a mixture of helium and neon, though other gases such as argon may be used.
The block of a ring laser gyroscope may contain at least one getter to maintain the purity of the lasing gas. The getter material absorbs non-inert gases both when the ring laser gyroscope is operational and when it is dormant. If the non-inert gases are not removed from the optical cavity, the lasing gas may degrade, which may reduce the efficiency of the laser. The degradation of the lasing gas may also impact the operational lifetime of the ring laser gyroscope.
The getter may consume oxygen during the lifetime of the gyroscope because oxygen is a non-inert gas. This consumption may cause a loss of oxygen in other components of the gyroscope that need oxygen to operate effectively. This may result in changed optical and electrical properties, which may also degrade the performance of the laser. If oxygen can be preserved in the system without affecting the purity of the lasing gas, the overall life of the gyroscope may be extended.
It would be desirable to restrict the rate at which a getter consumes impurities, while maintaining the purity of the lasing gas mixture.